Disappearing grooves mid way through cutting lacqures??

[pizzahotline]

Hi Folks,

Cutting lacquers on a Neumann VMS80

I've recently encountered an issue where the groove I'm cutting seems to disappear. It's only happened 3 times within the last couple of months after the lathe has been cutting beautifully for the last 2 years. When it happens, I recut the same album and it doesn't happen twice in the same place. Another thing to add is that it seems to happen at around the 50% - 80% mark. When I say that it 'disappears' what I mean is that the groove depth dramatically increases and then decreases for a couple of rotations, leading to the sylus coming out of the lacquer. Then, it returns to the lacquer and continues cutting. I've checked back at the source material and there doesn't seem to be any out of phase content that could be causing this. When you look back at this with a microscope the groove totally disappears and, if played back on a turntable, the stylus will simply jump out of the groove and stop tracking.

I've tried a few things to fix the issue and have a few theories. I thought it was a suction issue at first so I cleaned out the dust blockage in the platter by shooting compressed air up the pipe that goes from the swarf jar to the turntable, this blew huge chunks of dust and now the turntable suction has been improved dramatically. After doing this I didn't see the problem again for a good few weeks, only for it to reappear this week. Having said that, the groove didn't fully disappear this time, thankfully. My other theory is that the issue is caused by water or air bubbles in the dash pot, is this something people have experienced before?

Thanks for any help, it's always greatly appreciated.

[dmills]

Does the depth gauge reflect what is happening?
How about the current in the depth control coil?

If you cut a test with the damping test mode engaged does the resulting groove look right both at larger, smaller and at the diameter where the problem exists?

If you cut with the depth control disconnected and the amps turned off, do you get a sane groove? Note, you may need to wind the manual depth down to get a reasonable groove if running with no electrical depth control, remember to set this back afterward.

Just my immediate reaction, someone will be along shortly who recognises the exact issue.

[Maistrow]

Perhaps uneven lacquer coating on the disk. The coating may be thinning out in the areas on the disk surface where you are seeing this.

Maistrow

[pizzahotline]

Perhaps uneven lacquer coating on the disk. The coating may be thinning out in the areas on the disk surface where you are seeing this.

Maistrow

Good thinking. I was thinking the same but something that made me believe otherwise is it happening in similar places on different lacquers that are all from different batches. Also, If it was an uneven spot on a lacquer then It's unlikely that it would happen for just one single rotation, I would think that if it was a shallow section of lacquer then the same problem would effect adjacent grooves. I'll double check some things, thanks for the help!

[edge.technologies]

I dont know much about the cutting lathes but I know a whole bunch about ultra precision diamond turning machines. Something is happening intermittently (obviously), Is there a ground or room vibration happening. Slamming door. big truck rolling by outside, somebody doing jumping jacks or dropping a pallet on the floor next door, garbage truck dropping a dumpster? Other than atmospheric environmental disturbances, is the lathe completely clean? is the stylus securely mounted? maybe a slightly loose wire on the tracking mechanism?

[dubcutter89]

I mean is that the groove depth dramatically increases and then decreases for a couple of rotations

Funky!

it would happen for just one single rotation

Like one single 3mil wide strip of the blank is bad and everything else is fine? That's pretty narrow for mechanical thing!
Maybe good old VMS80 (turning 40 years) got dementia and its precise pitch/depth controller is loosing its mind...
Not uncommon for vintage electronics to not perform at factory specs after all these decades.

So if you're sure that it is not the mechanics, media or next door dance party it may need to go into lathe hospital for brain surgery

[pizzahotline]

I mean is that the groove depth dramatically increases and then decreases for a couple of rotations

Funky!

it would happen for just one single rotation

Like one single 3mil wide strip of the blank is bad and everything else is fine? That's pretty narrow for mechanical thing!
Maybe good old VMS80 (turning 40 years) got dementia and its precise pitch/depth controller is loosing its mind...
Not uncommon for vintage electronics to not perform at factory specs after all these decades.

So if you're sure that it is not the mechanics, media or next door dance party it may need to go into lathe hospital for brain surgery

Great point, let's hope she doesn't need any brain surgery though. I'm hoping it's an outside source making rumbles Thanks for your input

[gold]

Is there more resistance on the slide where the problem occurs? Is the slide well lubricated? When you fast wind over the problem area is the action as smooth as other spots? Those are the first questions I'd ask. I'd look for a mechanical issue first and then look for an electronics issue. It could be the automation but I think that's less likely.

[Maistrow]

This problem with the grooves has happened before. Many many years ago we manufactured lacquer for a company that made blank recording disk's for vinyl record production and the same thing was happening and we were able to correct it. After the lacquer is coated on the aluminum substrate, it quickly moves into a heat tunnel. The function of the heat tunnel is to "flash off" the aromatic solvents that are in the lacquer formula and this starts the curing process of the lacquer on the disk. If the heat tunnel is not set up correctly, or is too high or too low in temperature, you will get an uneven surface of lacquer on the disk. This where the lacquer has thinned out in different sectors on the disk where you are seeing the the disappearing grooves. But something to think about is this only happening on this batch of lacquers you are using and have you seen this issue before in the past or has anyone else having the same problems.

Maistrow

[pizzahotline]

Is there more resistance on the slide where the problem occurs? Is the slide well lubricated? When you fast wind over the problem area is the action as smooth as other spots? Those are the first questions I'd ask. I'd look for a mechanical issue first and then look for an electronics issue. It could be the automation but I think that's less likely.

Thanks for that info. I will definitely investigate the lead screw and related areas. What lubricant would you recommend? Also, is it important to remove oil from the lead screw and rails that the carriage slides on before re-oiling?

Thank you for your help!

[pizzahotline]

This problem with the grooves has happened before. Many many years ago we manufactured lacquer for a company that made blank recording disk's for vinyl record production and the same thing was happening and we were able to correct it. After the lacquer is coated on the aluminum substrate, it quickly moves into a heat tunnel. The function of the heat tunnel is to "flash off" the aromatic solvents that are in the lacquer formula and this starts the curing process of the lacquer on the disk. If the heat tunnel is not set up correctly, or is too high or too low in temperature, you will get an uneven surface of lacquer on the disk. This where the lacquer has thinned out in different sectors on the disk where you are seeing the the disappearing grooves. But something to think about is this only happening on this batch of lacquers you are using and have you seen this issue before in the past or has anyone else having the same problems.

Maistrow

Thanks for your reply. That's interesting to know more details about the lacquer processing. I hope that it is a problem with the laccqures and not the lathe I wish that I had saved the lacqures so I could go back and check to see if there were any dead spots. Thanks